Electrophotography is a useful process for printing images on a receiver (or “imaging substrate”), such as a piece or sheet of paper or another planar medium, glass, fabric, metal, or other objects as will be described below. In this process, an electrostatic latent image is formed on a photoreceptor by uniformly charging the photoreceptor and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern corresponding to the desired image (a “latent image”).
After the latent image is formed, charged toner particles are brought into the vicinity of the photoreceptor and are attracted to the latent image to develop the latent image into a visible image. Note that the visible image may not be visible to the naked eye depending on the composition of the toner particles (e.g., clear toner).
After the latent image is developed into a visible image on the photoreceptor, a suitable receiver is brought into juxtaposition with the visible image. A suitable electric field is applied to transfer the toner particles of the visible image to the receiver to form the desired print image on the receiver. The imaging process is typically repeated many times with reusable photoreceptors.
The receiver is then removed from its operative association with the photoreceptor and subjected to heat or pressure to permanently fix (“fuse”) the print image to the receiver. Plural print images, e.g., of separations of different colors, are overlaid on one receiver before fusing to form a multi-color print image on the receiver.
Electrophotographic (EP) printers typically transport the receiver past the photoreceptor to form the print image. The direction of travel of the receiver is referred to as the slow-scan, process, or in-track direction. This is typically the vertical (Y) direction of a portrait-oriented receiver. The direction perpendicular to the slow-scan direction is referred to as the fast-scan, cross-process, or cross-track direction, and is typically the horizontal (X) direction of a portrait-oriented receiver. “Scan” does not imply that any components are moving or scanning across the receiver; the terminology is conventional in the art.
Toner is required to be cleaned off members in EP printers for various reasons, including cleaning and maintenance. For example, residual or non-transferred toner is preferably cleaned off members of the printer so that it is not transferred to the receiver. When a receiver jams (paper jam), toner that would have been deposited on that receiver in normal operation is cleaned off members of the printer so that it does not contaminate components such as the transfer backup roller. Also, some printers deposit test patches used to monitor printer status; those patches are not intended for deposition on a receiver, so they are cleaned off the members on which they are deposited. However, toner can build up on cleaning members, resulting in image artifacts. For example, clumps of toner can build up behind a cleaning blade and break off when large enough; these clumps can travel through the printer and contaminate the member that was being cleaned or other members.
It is known to remove developer from a development member used to develop the latent image into the visible image. This can be useful for maintenance of a printer. U.S. Pat. No. 3,927,640 to Smith describes a magnetic gate for stopping developer flow when it is desired to purge the development system. U.S. Pat. No. 3,981,272 to Smith et al. describes a development system with a movable sump for storing developer. However, both of these schemes provide only off or on control, not variations in developer flow.
Commonly-assigned U.S. Pat. No. 7,502,581 to Jacobs et al., the disclosure of which is incorporated herein by reference, describes a movable metering blade for a magnetic brush development station to reduce build-up of contamination. However, this invention, although useful, also provides only two positions of the metering blade.
There is, therefore, a continuing need for a way of cleaning a rotatable member (e.g., a belt or drum) in an electrophotographic (EP) printer and reducing the occurrence of image artifacts resulting from cleaning.